The invention generally relates to the fields of communication systems and videoconferencing. More particularly, the invention is directed to methods and apparatus for reducing the bandwidth required to conduct a multipoint conference.
Telephone conferencing systems have been available for many years. These systems have primarily focused on providing audio conferencing. A typical conference includes a group of individuals who are telephonically connected into a discussion by an operator at a central locality. In recent years, however, the addition of video capabilities has greatly increased the bandwidth required to establish a multipoint audio-video conference.
By way of example, FIG. 1A illustrates a conventional network 10 for conducting an audio-video multipoint conference. The network 10 includes multiple personal conferencing systems (in this example, PCS 12a, PCS 12b, PCS 12c and PCS 12d) as well as a multimedia conference unit (MCU) 14 that is coupled to PCSs 12a-12d. In the situation where the PCSs 12a-12d are coupled over a local area network (LAN), the network 10 is illustrative of a conventional telephony-over-LAN (ToL) network. A PCS may be a video telephone, telephony-enabled computer, and/or portable device able to send and receive to each other directly via network 10, which may be a LAN or a wireless network.
Generally, the MCU 14 is capable of joining PCSs 12a-12d (ToL users in this specific example) in multipoint videoconferences. During a typical multipoint videoconference, the MCU 14 receives all video and audio signals from the participating PCSs and typically re-transmits the mixed audio signals of participating PCSs and the video signal originating from the dominant or presenting PCS to all participating PCSs, including the presenter. As seen in the example of FIG. 1A (which does not show audio signals but only shows video signals for simplicity), supposing PCS 12a is the presenter, the MCU 14 receives the audio signals and video signals from all PCSs 12a-12d, determines PCS 12a to be dominant, and then re-broadcasts the mixed audio signals and video signals originally from PCS 12a to PCSs 12a-12d. In this example, eight video connections (video signals 15a-15d from PCSs 12a-12d to MCU 14, and video signals 16a-19a from MCU 14 to PCSs 12a-12d, where video signals 16a-19a carry the video signals 15a sent from PCS 12a to MCU 14) between the MCU 14 and the PCSs 12a-12d via LAN hub 17 are required. This conventional system requires the MCU 14 to perform high level digital signal processing (DSP) of the multiple received and transmitted audio and video signals between all parties and MCU 14 involved in the videoconference. This high level of DSP analysis results in the MCU 14 being very expensive compared to an audio-only MCU, which is comparatively simple and inexpensive. Moreover, the use of eight video streams in addition to the audio connections normally used (not shown in FIG. 1A) results in heavy use of network bandwidth.
Another conventional approach to videoconferencing utilizes an MCU 14 capable of providing a multicast stream, as shown in the example of FIG. 1B. In the example of FIG. 1B (which does not show audio signals but only shows video signals for simplicity), supposing PCS 12a is presenting, MCU 14 receives the audio signals and video signals from all PCS 12a-12d, determines PCS 12a to be dominant, and then re-transmits the mixed audio signals and the video signals from PCS 12a to PCS 12b-12d in a multicast stream. In this example, the required video streams are reduced to five video streams (video signals 15a-15d from PCSs 12a-12d to MCU 14, and video multicast signal 20a from MCU 14 to PCSs 12b-12d, where video multicast signal 20a carries the video signals 15a originally sent from PCS 12a to MCU 14) between the MCU 14 and the PCSs 12a-12d via LAN hub 17, when the presenter PCS 12a views its own presentation. It should be noted that in those cases where the presenter PCS 12a wishes to view someone else""s presentation, an additional video stream (15b, shown in FIG. 1B as a dotted arrow from MCU 14 to LAN hub 17, where the dotted arrow 15b carries the video signal of a participant, e.g. PCS 12b, other than the presenter) from the MCU 14 to the PCS 12a via LAN hub 17 is required (and video 20a to PCS 12a would replace video 15b to PCS 12a), for a total of six video streams. Although the reduction in video streams from MCU multicast capability reduces the required DSP analysis somewhat, MCU 14 must still be capable of processing at least five video streams, which is still very expensive in comparison to an audio-only MCU.
In addition to requiring expensive processing power in the MCU 14, multiple audio and video streams for supporting the videoconference session require large network bandwidth resources, which may not be available in some circumstances when network traffic is heavy. Therefore, what is desired is an improved method and apparatus for reducing the bandwidth required to conduct a videoconference.
Broadly speaking, the invention relates to an improved method, apparatus and system for reducing the digital signal processing analysis required to support a multipoint conference call among a plurality of callers coupled via a network to a multimedia conference unit. The multimedia conference unit first determines which caller is a dominant caller, the other callers being subordinate callers. The multimedia conference unit then commands the subordinate callers to suppress a portion of their signals passed over the network. In some embodiments, the portion are video signals, and only the dominant caller transmits video signals to at least the subordinate callers either via the multimedia conference unit or directly to the subordinate callers, depending on whether point-to-point connection capability between callers exists.
In one embodiment, the callers pass audio signals and video signals over the network, and the multimedia conference unit uses the audio signals to determine which of the callers is dominant. In another embodiment, when the multimedia conference unit determines that the dominant caller has changed, the multimedia conference unit commands the previous dominant caller to stop sending video signals in the form of video packets and the new dominant caller, if not already sending video signals, to start sending video signals in the form of video packets.
These and other embodiments with advantages of the present invention will become apparent from the following detailed description and drawings.